1. Field of the Invention
The present invention relates to a video transfer system, and more particularly, to an error recovery method of a video transfer system that is capable of preventing a disturbance of a picture quality caused due to a packet delay and a packet loss.
2. Description of the Background Art
In general, when a mobile image is provided for service on a real time basis through the Internet by using an instrument such as a video phone, a packet delay and a packet loss takes place due to a non-isochronous nature of the Internet, and accordingly, a phenomenon occurs that an image of a frame of the receiving party is broken.
The image-damaging phenomenon can be solved to a degree by a post-processing, that is, an error concealment, at the receiving party, but without a method for fundamentally recovering an error, it is difficult to provide a high quality real-time based mobile image service.
In an effort to over come the problem of the mobile image service due to the error concealment, there have been proposed error recovery methods such as a re-transmission of a mobile image or a forward error correction. However, these methods are not suitable for a real time processing because they cause a long packet delay time. That is, these methods can't be adopted to such an instrument of a video phone.
On the other hand, there has been also provided an intra coding method in which when macro-blocks having a coefficient are transmitted in a general H.263 standard defined as international standard systems of video compression encoding, the macro-block is forcefully encoded in an inter mode (a predictive frame encoding mode) for minimum every 123rd. Encoding the macro-block in an “intra” mode is called an “intra” update.
An original purpose of the intra encoding method was to prevent accumulation of a mismatch of an inverse discrete cosine transform (IDCT).
But owing to its characteristics that it is not necessary to refer a previous picture, it has been adopted to a system using the most predictive video encoding, so as to be used as an alternative to restore an error or remove a propagation of a temporal error.
However, the conventional intra encoding method has the following problem.
That is, since it considers only a situation with no packet loss, that is, a situation without an error, the intra encoding method is not proper to be adopted to a video transfer system (the video phone) as it is in the aspect of an effective error restoration.
In addition, in case of a video transfer system adopting the conventional intra encoding method has a problem that, in case of a quick motion or when a scene is changed, if an image block is broken to be come a background region (that is, a not coded block), the background region is not intra-updated.
That is, the when the macro-block with a coefficient is transmitted, the macro-block can not be forcefully encoded in an intra mode for every 132nd at minimum.
Moreover, since a video transfer system adopting the conventional intra encoding method has a fixed refresh rate irrespective of an image state (a picture quality state) of the receiving party, it is not suitable as an error restoration method for a high quality video transfer.